docs: def make_thumbnail(file, size, bbox=None):
      '''
      Generate a thumbnail for a given image file.
  
      :param file file: The source image file to thumbnail
      :param int size: The thumbnail size in pixels (Thumbnails are squares)
      :param tuple bbox: An optionnal Bounding box definition for the thumbnail
      '''
      image = Image.open(file)
      if bbox:
          thumbnail = crop_thumbnail(image, size, bbox)
      else:
          thumbnail = center_thumbnail(image, size)
      return _img_to_file(thumbnail)